Torque sensor

ABSTRACT

A magnetism generation portion  4  is provided at a first shaft  2 , and a first magnetic yoke  7  and a second magnetic yoke  8  bent in L shape are provided at a second shaft  3  so that a magnetic flux generated at the magnetism generation portion  4  can be detected on the outer circumference side of the second shaft  3 , and a magnetism detecting device for detecting the magnetic flux can be provided on the outer circumference side of the second shaft.

BACKGROUND OF THE INVENTION

The present invention relates to a torque sensor suitable for use in apower steering device.

FIGS. 9 to 12 show a construction of a torque sensor 100 of aconventional art (shown in Patent Document 1, for example). FIG. 9 is aperspective view in the vicinity of the torque sensor. FIG. 10 is apartially enlarged view of FIG. 9. FIGS. 11 and 12 are diagrams forexplaining the action.

[Patent Document 1] Patent No. 3094049

In FIG. 9, the torque sensor 100 is provided between a first shaft 101and a second shaft 102. At the first shaft 101, a magnetism generationportion 103 for outputting a magnetic flux is provided. The magnetismgeneration portion 103 has a plurality of magnets 104 provided in thecircumferential direction around the first shaft 101. The magnets 104are magnetized toward the axis core direction (arrow direction) of thefirst shaft 101 and the adjoining magnets 104 are magnetized in thedirection opposite to each other, and thus, when the magnetismgeneration portion 103 is seen from the second shaft 102 side, as shownin FIG. 10, magnetic poles different from each other are adjoined. Thatis, S poles and N poles are arranged alternately.

As shown in FIG. 9, the second shaft 102 is provided with an outer ring105 and an inner ring 106, and as shown in FIG. 10, a plurality of outermagnetic path pieces 107 are extended from the outer ring 105, whileinner magnetic path pieces 108 are extended from the inner ring 106. Asshown in FIG. 10, a clearance 109 is provided between the outer ring 105and the inner ring 106, and a magnetic sensor 110 is arranged in theclearance 109.

Next, action will be described. Suppose that a driver does not steer asteering wheel. In this case, since the first shaft 101 is not rotatedwith respect to the second shaft 102, as shown in FIG. 11, each outermagnetic path piece 107 is opposed to the N pole and the S pole of themagnet 104 over the same area each, and each inner magnetic path piece108 is similarly opposed to the N pole and the S pole of the magnet 104over the same area each. In this case, the magnetic flux is not guidedto the outer magnetic path piece 107 and the inner magnetic path piece108, and the magnetic flux outputted from the N pole of the magnet 104is inputted to the S pole of the magnet 104. Therefore, the magneticflux sensor 110 does not detect the magnetic flux.

Next, suppose that the driver has steered the steering wheel. In thiscase, the first shaft 101 is rotated with respect to the second shaft102, and as shown in FIG. 12, the outer magnetic path piece 107 is movedto the S pole side, while the inner magnetic path piece 108 is moved tothe N pole side. In this case, since the magnetic flux outputted fromthe N pole of the magnet 104 reaches the S pole of the magnet 104 viathe inner magnetic path piece 108, the inner ring 106, the magneticsensor 110, the outer ring 105, and the outer magnetic path piece 107, arotation amount of the first shaft 101 with respect to the second shaft102, that is, a steering torque of the steering wheel can be detectedbased on the magnetic flux amount detected by the magnetic sensor 110.

In the above-mentioned background art, since the torque sensor 100 is inthe structure that it is provided between the first shaft 101 and thesecond shaft 102 in the axial direction, the entire length is long inthe axial direction due to a space in which the torque sensor 100 isarranged. Thus, the torque sensor 100 which can be accommodated in thecompact manner in the axial direction has been in demand.

The present invention was made in view of the problems of the backgroundart and has an object to provide a torque sensor which can reduce thelength in the axial direction when it is attached to two shafts whosetorque is to be detected.

SUMMARY OF THE INVENTION

The present invention is a torque sensor comprising a housing, a firstshaft and a second shaft accommodated in the housing and connectedcoaxially by a torsion bar, and a magnetism generation portion attachedto the first shaft so as to surround the outer circumference of thefirst shaft and outputting a magnetic flux in the axis core direction ofthe first shaft, in which

a plurality of magnetic yoke portions comprising a first magnetic yokeand a second magnetic yoke for guiding the magnetic flux outputted fromthe magnetism generation portion are attached to the second shaft; and

a torque between the first shaft and the second shaft is detectedmagnetically by a magnetic sensor through detection of the magnetic fluxin a magnetic gap between the first magnetic yoke and the secondmagnetic yoke,

wherein the first magnetic yoke and the second magnetic yoke have theirone end opposed to the magnetism generation portion, respectively, andthe first magnetic yoke and the second magnetic yoke are bent in the Lshape in the middle and extended in the direction crossing the axis coreof the second shaft, respectively, and the other ends of the firstmagnetic yoke and the second magnetic yoke are provided separately fromeach other in the axis core direction on the outer circumference side ofthe second shaft;

the other ends of the first magnetic yokes of each magnetic yoke portionare connected to each other by a first magnetic ring;

the other ends of the second magnetic yokes of each magnetic yokeportion are connected to each other by a second magnetic ring; and

the magnetic sensor is provided in the magnetic gap between the firstmagnetic ring and the second magnetic ring.

According to the present invention, since it is so constructed that themagnetic flux outputted from the magnetism generation portion is guidedoutward in the radial direction of the shaft so that change in themagnetic flux with change of a steering torque of a steering wheel isdetected on outside in the radial direction of the shaft, a magnetismdetecting device provided with a magnetic sensor can be arranged outsidein the radial direction of the shaft and the construction can be formedwith compact length in the axial direction.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the principle of the present invention;

FIG. 2 is a diagram for explaining action;

FIG. 3 is a diagram for explaining action;

FIG. 4 is an end face view in a state where a first magnetic yoke, asecond magnetic yoke, a first magnetic ring and a second magnetic ringare molded to a resin and a sleeve is assembled thereto;

FIG. 5 is an A-A sectional view of FIG. 2;

FIG. 6 is a B-B sectional view of FIG. 2;

FIG. 7 is a C-C sectional view of FIG. 2;

FIG. 8 is a longitudinal sectional view of an electric power steeringdevice;

FIG. 9 is a perspective view of the vicinity of a torque sensor(conventional art);

FIG. 10 is a partial enlarged view of FIG. 7 (conventional art);

FIG. 11 is a diagram for explaining action (conventional art); and

FIG. 12 is a diagram for explaining action (conventional art).

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

A principle of the present invention will be described based on theattached drawings. FIG. 1 explains an example used when a torque sensor1 of the present invention is applied to an electric power steeringdevice for detecting a torque between an input shaft 2 and an outputshaft 3. The input shaft 2 and the output shaft 3 are stored in ahousing H.

To the input shaft 2, a steering force is given by the steering wheel.The output shaft 3 gives a steering assisting force to the steeredsystem side. The input shaft 2 and the output shaft 3 are connected toeach other by a torsion bar.

At the input shaft 2, a magnetism generation portion 4 is provided. Themagnetism generation portion 4 is in the structure that a magnet portion6 is provided at a back yoke 5 formed by an annular magnetic body. Themagnet portion 6 is formed by magnetizing the magnetic body toward theaxis core direction of the input shaft 2 and in the circumferentialdirection, it is magnetized so that N poles and S poles are arrangedalternately as shown in FIG. 1.

At the output shaft 3, a magnetic yoke portion 9 constructed by a firstmagnetic yoke 7 and a second magnetic yoke 8 are provided. The magneticyoke portion 9 is provided on the outer circumference of the outputshaft 3 in plural toward the circumferential direction. The firstmagnetic yoke 7 is formed by a straight portion 10 and a crossingportion 11 crossing the straight portion 10 and bent in the L shape. Thestraight portion 10 of the first magnetic yoke 7 is provided along theaxial direction, and one end of the first magnetic yoke 7 is faced withthe magnet portion 6. Also, the crossing portion 11 of the firstmagnetic yoke 7 is provided in the radial direction, while the other endof the first magnetic yoke 7 is faced outward in the radial direction ofthe output shaft 3.

Also, the second magnetic yoke 8 is formed by a straight portion 12 anda crossing portion 13 crossing the straight portion 12 and bent in the Lshape. The straight portion 12 of the second magnetic yoke 8 is providedalong the axial direction, and one end of the second magnetic yoke 8 isfaced with the magnet portion 6. Also, the crossing portion 13 of thesecond magnetic yoke 8 is provided in the radial direction, while theother end of the second magnetic yoke 7 is faced outward in the radialdirection of the output shaft 3. The other end of the first magneticyoke 7 and the other end of the second magnetic yoke 8 are separatedfrom each other in the axis core direction of the output shaft 3.

The other ends of the first magnetic yokes 7 of each magnetic yokeportion 9 are connected to each other by a first magnetic ring 14, whilethe other ends of the second magnetic yokes 8 of each magnetic yokeportion 9 are connected to each other by a second magnetic ring 15.

Outside the first magnetic ring 14, a first magnetism collecting ring 17is provided on the inner surface of the housing H so as to surround thefirst magnetic ring 14. The magnetism collecting ring 17 is formed by amagnetic body and constitutes a part of a magnetic circuit. The firstmagnetism collecting ring 17 is in the shape that a plate material isbent in an annular state. The width in the axial direction of the firstmagnetism collecting ring 17 is formed larger than the width in theaxial direction of the first magnetic ring 14. Also, outside the secondmagnetic ring 15, a second magnetism collecting ring 18 is provided onthe inner surface of the housing H so as to surround the second magneticring 15. The second magnetism collecting ring 18 is formed by a magneticbody and constitutes a part of the magnetic circuit. The secondmagnetism collecting ring 18 is in the shape that a plate material isbent in the annular state. The width in the axial direction of thesecond magnetism collecting ring 18 is formed larger than the width inthe axial direction of the second magnetic ring 15.

A first magnetism collecting yoke 19 is provided at the first magnetismcollecting ring 17, while a second magnetism collecting yoke 20 isprovided at the second magnetism collecting ring 18. At the firstmagnetism collecting yoke 19 and the second magnetism collecting yoke20, two pairs of projections 21, 22, 23, 24 are provided so that theyare opposed to each other. A magnetic gap is formed between each pair ofprojections 21, 22, 23, 24, and magnetic sensors 25, 26 are arranged inthe magnetic gaps. A magnetic gap forming portion is constructed by thefirst magnetism collecting yoke 19, the second magnetism collecting yoke20, the pairs of projections 21, 22, 23, 24.

Next, action will be described. In the state where the steering wheel isnot steered, as shown in FIG. 2, the centers of one ends of the firstmagnetic yoke 7, the second magnetic yoke 8 are located at the boundarybetween the N pole and the S pole with each one end extending over the Npole and the S pole of the magnet portion 6 so that each one end isfaced with the N pole and the S pole by the same area.

As shown in FIG. 2, in this state, the magnetic flux outputted from theN pole is not guided by the first magnetic yoke 7 and the secondmagnetic yoke 8 but inputted to the S pole of the magnet portion 6.Therefore, the magnetic sensors 25, 26 shown in FIG. 1 do not detect themagnetic flux.

Next, suppose that the driver steers the steering wheel. In this case,since the input shaft 2 is rotated with respect to the output shaft 3,as shown in FIG. 3, the center of one end of the first magnetic yoke 7is moved to the N pole side, the area of the one end facing the N poleof the magnet portion 6 becomes larger than the area facing the S poleof the magnet portion 6. Also, the center of one end of the secondmagnetic yoke 8 is moved to the S pole side and the area of the one endfacing the S pole of the magnet portion 6 becomes larger than the areafacing the N pole of the magnet portion 6. In this case, in the firstmagnetic yoke 7, after the magnetic flux outputted from the N pole ofthe magnet portion 6 is inputted, the magnetic flux goes through amagnetic circuit of the first magnetic ring 14, the first magnetismcollecting ring 17, the first magnetism collecting yoke 19, theprojections 22, 24, the magnetic sensor 25, 26, the projections 21, 23,the second magnetism collecting yoke 20, the second magnetism collectingring 18, the second magnetic ring 15, the second magnetic yoke 8 to theS pole of the magnet portion 6 as shown in FIG. 1.

The amount of the magnetic flux detected at the magnetic sensors 25, 26corresponds to the area of the one end of the first magnetic yoke 7facing the N pole of the magnet portion 6 and the area of the one end ofthe second magnetic yoke 8 facing the S pole of the magnet portion 6.Therefore, from the amount of the magnetic flux detected at the magneticsensors 25, 26, movement amounts of the first magnetic yoke 7 and thesecond magnetic yoke 8, that is, the steering torque of the steeringwheel rotating the input shaft 2 can be detected.

In this way, since the first magnetic yoke 7 and the second magneticyoke 8 are bent in the L shape so that they can guide the magnetic fluxoutputted from the magnetism generation portion 4 to the outercircumference side of the output shaft 3 and a magnetism detectingdevice provided with the magnetic sensors 25, 26 can be provided on theouter circumference side of the output shaft 3, the length of the inputshaft 2 and the output shaft 3 in the axial direction can be formedshort.

Also, the first magnetism collecting ring 17, the second magnetismcollecting ring 18 are provided facing the first magnetic ring 14, thesecond magnetic ring 15 outside each of the first magnetic ring 14, thesecond magnetic ring 15 so as to surround the first magnetic ring 14,the second magnetic ring 15. Therefore, even if the first magnetic ring14 and the second magnetic ring 15 are eccentric with each other, allthe magnetic fluxes passing through the first magnetic ring 14 and thesecond magnetic ring 15 can be efficiently guided to the first magnetismcollecting ring 17 and the second magnetism collecting ring 18.Moreover, since the first magnetism collecting ring 17 and the secondmagnetism collecting ring 18 are formed wider in the axial directionthan the first magnetic ring 14 and the second magnetic ring 15,respectively, the magnetic flux having passed through the first magneticring 14 and the second magnetic ring 15 are more efficiently guided tothe first magnetism collecting ring 17 and the second magnetismcollecting ring 18.

Also, the first magnetism collecting ring 17 and the second magnetismcollecting ring 18 are formed wider than the first magnetic ring 14 andthe second magnetic ring 15 respectively, outside the first magneticring 14 and the second magnetic ring 15, respectively. Therefore, evenif there is an error of positional displacement in the direction alongthe axis core between the first magnetic ring 14 and the first magnetismcollecting ring 17 as well as the second magnetic ring 15 and the secondmagnetism collecting ring 18, the first magnetism collecting ring 17 canbe faced with the first magnetic ring 14, and the second magnetismcollecting ring 18 can be faced with the second magnetic ring 15.Therefore, a loss of the magnetic flux between the first magnetismcollecting ring 17 and the first magnetic ring 14 as well as the secondmagnetic collecting ring 18 and the second magnetic ring 15 can besuppressed, and efficient transmission is achieved.

Also, the magnetic flux outputted from the N pole of the magnet portion6 faced with the first magnetic yoke 7 goes through the plurality offirst magnetic yokes 7, the first magnetic ring 14, the first magnetismcollecting ring 17, the second magnetism collecting ring 18, the secondmagnetic ring 15, the plurality of second magnetic yokes 8 and in themiddle of the way to the S pole of the magnet portion 6 faced with thesecond magnetic yoke 8, it goes through the magnetic sensors 25, 26,being concentrated with a high density between the projections 22, 24 ofthe first magnetism collecting yoke 19 and the projections 21, 23 of thesecond magnetism collecting yoke 20. Thus, the magnetic sensors 25, 26can detect change in the magnetic flux with operation of the steeringwheel efficiently and with high accuracy.

FIGS. 4 to 7 show a sleeve assembly 32 in which a sleeve 31 is providedat a yoke mold body 30 where the first magnetic yoke 7, the secondmagnetic yoke 8, the first magnetic ring 14 and the second magnetic ring15 are molded to a resin. FIG. 4 shows an end face view of the sleeveassembly 32, FIG. 5 shows an A-A sectional view of FIG. 4, FIG. 6 is aB-B sectional view of FIG. 4 and FIG. 7 is a C-C sectional view of FIG.4.

As shown in FIGS. 5 to 7, the sleeve 31 is in the shape inserted intothe yoke mold body 30 from the tip end side and the rear end side of thesleeve 31 is constructed so that the yoke mold body 30 is exposed to theoutside. The sleeve 31 is, as will be described later, press-fitted intothe output shaft 3 when the sleeve assembly 32 is assembled to theoutput shaft 3.

As mentioned above, since a resin is not provided on the outercircumference of the rear end side of the sleeve 31, there is no fearthat the resin is damaged even if the diameter of the sleeve 31 isexpanded at press fitting of the sleeve 31 into the output shaft 3, andmoreover, the force to expand the diameter of the sleeve 31 is rarelyleft as a stress in the resin.

In the above embodiment shown in FIG. 1, the desired object of thepresent invention can be achieved even after the first magnetismcollecting ring 17, the second magnetism collecting ring 18, the firstmagnetism collecting yoke 19 and the second magnetism collecting yoke 20are deleted, a space between the first magnetic ring 14 and the secondmagnetic ring 15 is made as a magnetic gap and the magnetic sensors 25,26 are provided in the magnetic gap.

However, when it is constructed as in the above described manner in theembodiment shown in FIG. 1, the following working effect is exerted.When the first magnetism collecting ring 17, the second magnetismcollecting ring 18 are not provided but the magnetic gap is providedbetween the first magnetic ring 14 and the second magnetic ring 15 so asto detect the magnetic flux in the magnetic gap by the magnetic sensors25, 26, if the first magnetic ring 14 and the second magnetic ring 15are not assembled in parallel with each other with high accuracy, aninterval of the magnetic gap is changed due to change in the width ofthe clearance between the first magnetic ring 14 and the second magneticring 15 with rotation of the input shaft 2 and the output shaft 3,detection of the magnetic flux is affected. That is, due to influence ofan error in assembling of the first magnetic ring 14 and the secondmagnetic ring 15, magnetic detection of the rotation of the output shaft3 with respect to the input shaft 2 with accuracy becomes difficult.

On the other hand, in the above embodiment shown in FIG. 1, outside thefirst magnetic ring 14 and the second magnetic ring 15, the firstmagnetism collecting ring 17 and the second magnetism collecting ring 18are provided in the housing H, respectively, the first magnetismcollecting yoke 19 and the second magnetism collecting yoke 20 areprovided at the first magnetism collecting ring 17 and the secondmagnetism collecting ring 18, and two pairs of projections 21 to 24 areprovided at the first magnetism collecting yoke 19 and the secondmagnetism collecting yoke 20 so that spaces between these two pairs ofthe projections 21 to 24 are made as the magnetic gaps, and the firstmagnetism collecting ring 17 and the second magnetism collecting ring 18are mounted to the housing H and fixed. Therefore, the interval of themagnetic gap is not affected by rotation of the input shaft 2 and theoutput shaft 3 but constant. That is, in the case of the aboveembodiment shown in FIG. 1, not affected by the rotation of the inputshaft 2 and the output shaft 3, detection can be made while reducing anerror of the steering force of the steering wheel.

FIG. 8 shows a longitudinal sectional view of an electric power steeringdevice 40 incorporating the above torque sensor 1. In the housing H, theinput shaft 2 and the output shaft 3 are arranged vertically, and theinput shaft 2 and the output shaft 3 are rotatably supported in thehousing H by bearings 41, 42. The input shaft 2 is formed in thecylindrical shape, and a torsion bar 43 is arranged inside. The torsionbar 43 is connected to the input shaft 2 by a pin 44 at the upper end.

The lower end side of the torsion bar 43 is connected to the outputshaft 3 through a serration 44.

To the input shaft 2, the magnetism generation portion 4 is mounted. Themagnetism generation portion 4 is provided with a back yoke 46 formedwith a shaft insertion hole 45 at the center and formed from an annularmagnetic body and the magnet portion 6 attached to the back yoke 46. Theback yoke 46 is a member formed from a magnetic body and functioning asa magnetic path.

Also, at the output shaft 3, the sleeve assembly 32 is press-fitted andmounted. The sleeve assembly 32 is assembled to the upper end of theoutput shaft 3 so that the sleeve 31 is press-fitted to the upper end ofthe output shaft 3. The sleeve 31 is formed by a non-magnetic body sothat the magnetic flux generated at the magnetism generation portion 4does not leak to the output shaft 3 side.

As shown in FIG. 8, in the state where the sleeve assembly 32 isassembled to the output shaft 3, one ends of the first magnetic yoke 7and the second magnetic yoke 8 are faced with the magnet portion 6 ofthe magnetism generation portion 4 with a slight gap between them.

On the inner face of the housing H, the first magnetism collecting ring17 and the second magnetism collecting ring 18 are attached. The firstmagnetism collecting ring 17 is formed wider than the first magneticring 14 and faced with the first magnetic ring 14. The second magnetismcollecting ring 18 is formed wider than the second magnetic ring 15 andfaced with the second magnetic ring 15.

In the housing H, a magnetism detecting device mounting hole 47 isformed, and a magnetism detecting device 48 is attached to the magnetismdetecting device mounting hole 47. The magnetism detecting device 48 isprovided with the magnetic sensors 25, 26 and incorporates a calculationportion and the like for calculating a magnetic flux amount based on theoutputs of the magnetic sensors 25, 26.

In the magnetism detecting device mounting hole 47, the first magnetismcollecting yoke 19 is mounted to the first magnetism collecting ring 17.Also, the second magnetism collecting yoke 20 is mounted to the secondmagnetism collecting ring 18. At the first magnetism collecting yoke 19and the second magnetism collecting yoke 20, the projections 21, 23, 22,24 (shown in FIG. 1) are provided so that they are opposed to eachother. Between the projections 21, 23, 22, 24 opposed to each other, themagnetic sensors 25, 26 are arranged.

In the above description, the case where the torque sensor 1 is appliedto the electric power steering device 40 has been described, but notlimited to the electric power steering device 40, it can be widelyapplied for detection of a torque between two shafts.

1. A torque sensor comprising a housing, a first shaft and a secondshaft accommodated in the housing and connected coaxially by a torsionbar, and a magnetism generation portion attached to the first shaft soas to surround the outer circumference of the first shaft and outputtinga magnetic flux in the axis core direction of the first shaft, in whicha plurality of magnetic yoke portions comprising a first magnetic yokeand a second magnetic yoke for guiding the magnetic flux outputted fromthe magnetism generation portion are attached to the second shaft; and atorque between the first shaft and the second shaft is detectedmagnetically by a magnetic sensor through detection of the magnetic fluxin a magnetic gap between the first magnetic yoke and the secondmagnetic yoke, wherein the first magnetic yoke and the second magneticyoke have their one end opposed to the magnetism generation portion,respectively, and the first magnetic yoke and the second magnetic yokeare bent in the L shape in the middle and extended in the directioncrossing the axis core of the second shaft, respectively, and the otherends of the first magnetic yoke and the second magnetic yoke areprovided separately from each other in the axis core direction on theouter circumference side of the second shaft; the other ends of thefirst magnetic yokes of each magnetic yoke portion are connected to eachother by a first magnetic ring; the other ends of the second magneticyokes of each magnetic yoke portion are connected to each other by asecond magnetic ring; and the magnetic sensor is provided in themagnetic gap between the first magnetic ring and the second magneticring.
 2. The torque sensor, wherein a first magnetism collecting ring isprovided opposite to the first magnetic ring in the housing; a secondmagnetism collecting ring is provided opposite to the second magneticring in the housing; and a magnetic gap forming portion for forming themagnetic gap is provided between the first magnetism collecting ring andthe second magnetism collecting ring.
 3. The torque sensor according toclaim 2, wherein the first magnetism collecting ring is provided widerthan the first magnetic ring and the second magnetism collecting ring isprovided wider than the second magnetic ring.
 4. The torque sensoraccording to claim 2 or 3, wherein the magnetic gap forming portion isprovided with a first magnetism collecting yoke connected to the firstmagnetism collecting ring, a second magnetism collecting yoke connectedto the second magnetism collecting ring, and two pairs of projectionsprovided at the first magnetism collecting yoke and the second magnetismcollecting yoke, wherein each magnetic gap is made between these twopairs of the projections and each magnetic sensor is provided in eachmagnetic gap.